The present invention relates to turbochargers for use in internal combustion engines, and, more particularly, to a turbocharger having an integrated cooling system.
A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for proper operation of an engine.
An internal combustion engine, therefore, may include one or more turbochargers for compressing air to be supplied to one or more combustion chambers within corresponding combustion cylinders. The turbocharger supplies combustion air at a higher pressure and higher density than existing atmospheric pressure and ambient density. The use of a turbocharger can compensate for lack of power due to altitude, or to increase the power that can be obtained from an engine of a given displacement, thereby reducing the cost, weight and size of an engine required for a given power output.
Each turbocharger typically includes a turbine driven by exhaust gases from the engine, and a compressor driven by the turbine. The compressor receives the air to be compressed and supplies the air to the combustion chamber. It is known to provide higher compression levels through the use of a multi-stage turbocharger. A known multi-stage turbocharger includes a turbine and compressor section having two or more compressors. A common shaft interconnects the turbine wheel of the turbine with compressor wheels in the compressor section. A stream of exhaust gases from the engine is conducted from the exhaust manifold to the turbine. The stream of exhaust gases passing through the turbine causes the turbine wheel to rotate, thereby turning the common shaft interconnecting the turbine wheel and the compressor wheels and rotating the compressor wheels.
Ambient air to be used for combustion in the internal combustion engine is brought into the compressor section, through an inlet for the first compressor. The air is compressed by the first compressor wheel, and passes from the first compressor through a first compressor outlet and an interstage duct to the inlet of the second compressor in the compressor section, for farther compression. The out flow from the second compressor exits the compressor section of the turbocharger at the second compressor outlet, and is directed to the inlet manifold of the internal combustion engine.
Several problems are experienced with previously known constructions for turbochargers as described above. Compressing the air in the first compressor significantly raises the temperature of the air, increasing the power required by the second compressor to achieve a desire pressure boost. To overcome the detrimental effects of the increase in temperature, so-called xe2x80x9cintercoolersxe2x80x9d have been provided in the flow path between the first compressor outlet and the second compressor inlet. A known intercooler is a remote unit, often somewhat distant from the turbocharger, increasing the complexity of the turbocharger system and the ducting for gas flow between compressors. Similarly, so-called xe2x80x9caftercoolersxe2x80x9d have been used after the second compressor, to cool the compressed air supplied to the intake manifold. Cooling compressed air supplied to the intake manifold increases the oxygen content per unit volume to better support combustion in the cylinders, and decreases engine operating temperatures. High engine operating temperature has been associated with higher emission levels from the engine. Again, known designs for aftercoolers have included satellite heat exchangers which have added to the complexity of the turbocharger system.
U.S. Pat. No. 3,829,235 (Woollenweber, Jr.) discloses a single stage turbocharger compressor in which vanes are formed to provide frontal vane portions extending radially beyond adjoining vane portions. An internal wall of the compressor cover forms two discrete passages, one for air flow induced by the radially extending vanes, which is at low temperature and low pressure; and the other for flow induced by the adjoining vane portions which is at high temperature and higher pressure. Heat exchange may occur across the wall between the two air flow paths, before both air flows are directed to an external heat exchanger.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with a plurality of combustion cylinders; an exhaust manifold associated with the combustion cylinders; and an intake manifold associated with the combustion cylinders. A turbocharger includes a shaft; a turbine having a turbine casing, and a turbine wheel disposed on the shaft in the turbine housing. A turbine inlet and a turbine outlet in the casing are associated with the turbine wheel. The turbine inlet is connected in fluid flow communication with the exhaust manifold. A compressor section has an inlet and an outlet, the inlet associated with a source of combustion gas, and the outlet associated with the intake manifold. A cooling system has a cooling air shroud at least partially surrounding the compressor section. The cooling air shroud has a cooling air inlet and a cooling air outlet. A fan is drivingly connected to the shaft and operatively disposed in the cooling air inlet.
In another aspect of the invention, a turbocharger is provided with a shaft; a turbine including a turbine casing, a turbine wheel mounted on the shaft in the casing and a turbine inlet and a turbine outlet in the casing associated with the turbine wheel. A compressor section includes a first compressor having a first compressor casing, a first compressor wheel disposed on the shaft in the first compressor casing, and a first compressor inlet and first compressor outlet in the first compressor casing associated with the first compressor wheel. A cooling air shroud has a cooling air inlet and a cooling air outlet. A fan is drivingly connected to the shaft.
In yet another aspect of the invention, a method is provided for cooling a turbocharger having a shaft, a turbine wheel operatively disposed on the shaft for rotating the shaft, and a compressor section having a compressor wheel mounted on the shaft and a compressor casing defining an inlet and an outlet, the method comprises steps of providing a cooling air shroud; providing a cooling air inlet and a cooling air outlet for the cooling air shroud; providing a fan operatively disposed in the cooling air shroud; rotating the fan by rotation of the shaft; and circulating cooling air through the cooling air shroud in heat exchange relationship with compressed gas flowing through the compressor section.